Non-surgical device and methods for trans-esophageal vagus nerve stimulation

ABSTRACT

Devices and methods of non-surgically providing vagus nerve therapy trans-esophageally to treat a variety of medical conditions are disclosed herein. In an embodiment, an implantable medical device comprises a support member having an outer surface. The support member is adapted to engage the inner wall of an esophagus. The IMD also comprises at least one electrode disposed on the outer surface of the support member. The at least one electrode is capable of applying a trans-esophageal electrical signal to the vagus nerve through the wall of the esophagus from the inner lumen thereof. The implantable medical device further comprises a signal generator coupled to the support member and to the at least one electrode. The signal generator causes the at least one electrode to apply an electrical signal to the vagus nerve to treat a medical condition.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a related application to U.S. patent applicationSer. No. 11/796,058, entitled “Trans-Esophageal Vagus NerveStimulation,” which is filed on the same day as the present applicationand in the name of the same inventors.

BACKGROUND

1. Technical Field

The subject matter of this disclosure generally relates to the field ofmedical devices. More specifically, the present disclosure relates tonon-surgically implantable medical devices and methods for implementingvagus nerve therapy.

2. Background Information

Many advancements have been made in treating medical conditionsinvolving or mediated by the neurological systems and structures of thehuman body. In addition to drugs and surgical intervention, therapiesusing electrical signals for modulating the electrical activity of thebody have been found to be effective. In particular, medical deviceshave been effectively used to deliver therapeutic electrical signals tovarious portions of a patient's body (e.g., the vagus nerve) fortreating a variety of medical conditions. Electrical signal therapy maybe applied to a target portion of the body by an implantable medicaldevice (IMD) that is located inside the patient's body or,alternatively, may be applied by devices located external to the body.In addition, some proposed devices include a combination of implantedand external components.

The use of medical devices to provide electrical signal therapy hasincreased rapidly in recent decades. Such devices include pacemakers anddefibrillators, which provide electrical signal therapy to heart tissue,as well as spinal cord stimulators for treatment of pain. In addition,devices have also been approved to provide electrical signal therapy tothe vagus nerve (the 10^(th) cranial nerve) to treat epilepsy anddepression. Additional medical devices for providing electrical signaltherapy have been proposed for stimulation of other nerves, such as thesympathetic nerve, the phrenic nerve and the occipital nerve.

The vagus nerve (cranial nerve X) is the longest nerve in the humanbody. It originates in the brainstem and extends, through the jugularforamen, down below the head, to the abdomen. Branches of the vagusnerve innervate various organs of the body, including the heart, thestomach, the lungs, the kidneys, the pancreas, and the liver. In view ofthe vagus nerve's many functions, a medical device such as an electricalsignal generator has been coupled to a patient's vagus nerve to treat anumber of medical conditions. In particular, electrical signal therapyfor the vagus nerve, often referred to as vagus nerve stimulation (VNS),has been approved in the United States and elsewhere to treat epilepsyand depression. Application of an electrical signal to the vagus nerveis thought to affect some of its connections to areas in the brain thatare prone to seizure activity. Because of the vagus nerve's innervationof the stomach, stimulating the vagus nerve may also be therapeuticallybeneficial to treating eating disorders such as bulimia nervosa, as wellas treating morbid obesity.

Current and proposed VNS treatments have involved surgically couplingelectrodes to the left and/or right vagus nerves in the neck. Othertreatments involve surgically implanting electrodes to one or moresurfaces in the abdomen, such as by laparoscopic surgery through thepatient's abdominal wall. Electrical signal therapies in addition to VNShave been proposed to treat eating disorders such as obesity. Thesetechniques include coupling electrodes to the exterior and/or interiorof the stomach, duodenum, or intestinal walls. However, all of theaforementioned therapies either do not provide stimulation directedspecifically to the vagus nerve, substantially interfere with normalgastrointestinal function, require some type of invasive surgery, or allof the above.

Consequently, there is a need for non-surgical devices and methods fortreating medical conditions. There is also a need for providing aneasily implanted device that provides little or no interference withnormal gastrointestinal function. There is also a need to provideimproved methods and devices for vagus nerve stimulation, and to avoidundesired side effects associated with conventional surgical vagus nervestimulation.

BRIEF SUMMARY

The present invention provides devices and methods for non-surgicallyproviding vagus nerve therapy to treat a variety of medical conditions.Embodiments of an IMD provide electrical stimulation to the vagus nervethrough the wall of the esophagus (i.e. trans-esophageally) via a devicecoupled to the inner surface of the esophagus. Furthermore, implantationof the IMD may be accomplished non-surgically by oral insertion,precluding the need for incisions or even laparoscopic surgery.

In an embodiment, an implantable medical device for providing atherapeutic electrical signal to a vagus nerve of a patient comprises asupport member having an outer surface. The support member is adapted toengage the inner wall of an esophagus. The IMD also comprises at leastone electrode disposed on the outer surface of the support member. Theat least one electrode is adapted to apply a trans-esophageal electricalsignal to a vagus nerve through the wall of the esophagus from the innerlumen thereof. The implantable medical device further comprises a signalgenerator coupled to the support member and to the at least oneelectrode. The signal generator generates the electrical signal forapplication to the vagus nerve to treat a medical condition.

In another embodiment, an implantable medical device comprises a supportmember having an outer surface adapted to engage an inner surface of anesophagus of a patient. The implantable medical device comprises atleast one electrode coupled to the outer surface of the support member.The at least one electrode is adapted to apply an electrical signal to avagus nerve through the wall of the esophagus. Additionally, theimplantable medical device comprises a signal generator coupled to thesupport member and to the at least one electrode. The signal generatoris capable of generating an electrical signal for application to a vagusnerve of the patient. Furthermore, the implantable medical devicecomprises a power supply coupled to said support member and to thesignal generator. The power supply is capable of providing electricalpower to the signal generator.

In yet another embodiment, a medical device system comprises a supportmember having an outer surface. The outer surface is adapted to engagean inner surface of an esophagus of a patient. The system also comprisesat least one electrode coupled to the outer surface of the supportmember and adapted to apply a therapeutic electrical signaltrans-esophageally to a vagus nerve of the patient. Furthermore, thesystem comprises a signal generator coupled to the support member and tothe at least one electrode. The signal generator is capable ofgenerating said electrical signal for application to a vagus nerve. Inaddition, the system comprises a power supply for providing electricalpower to said signal generator. The system also comprises an externalprogramming system for programming one or more parameters defining saidtherapeutic electrical signal.

In an embodiment, a method of providing electrical signal therapy to avagus nerve of a patient comprises implanting a medical device whichincludes at least one electrode in the lumen of the abdominal portion ofthe esophagus of the patient such that the at least one electrode is incontact with the surface of the esophagus wall. The method furthercomprises applying an electrical signal to at least one vagus nerve ofthe patient through the wall of the esophagus to treat a medicalcondition of the patient.

In another embodiment, a method of providing electrical signal therapyto a vagus nerve of a patient comprises using an ambulatory medicaldevice to apply an electrical signal trans-esophageally to a vagus nerveof the patient from inside the abdominal portion of an esophagus.

In another embodiment, a method of providing an electrical signaltherapy to a vagus nerve of a patient comprises providing an ambulatorymedical device, which in turn comprises a support member having an outersurface, at least one electrode on the outer surface of the supportmember, and an electrical signal generator coupled to the support memberand to the at least one electrode. The method further comprisesnon-surgically implanting the ambulatory medical device, generating atherapeutic electrical signal using the electrical signal generator, andapplying the therapeutic electrical signal trans-esophageally to a vagusnerve of a patient from inside the abdominal portion of the patient'sesophagus.

The foregoing has broadly outlined certain features and technicaladvantages of the invention in order that the detailed description ofembodiments of the invention that follows may be better understood.Additional features and advantages of embodiments of the invention willbe described hereinafter that form the subject of the claims of theinvention. It should be appreciated by those skilled in the art that theconception and the specific embodiments disclosed may be readilyutilized as a basis for modifying or designing other structures forcarrying out the same purposes of the invention. It should also berealized by those skilled in the art that such equivalent constructionsdo not depart from the spirit and scope of the invention as set forth inthe appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of the preferred embodiments of theinvention, reference will now be made to the accompanying drawings inwhich:

FIG. 1 depicts, in schematic form, an embodiment of an implantablemedical device (IMD) system comprising an IMD implanted within a patientand an external device for programming the IMD and, in an alternativeembodiment, providing power to the IMD;

FIG. 2 illustrates an enlarged view of an embodiment of the IMDimplanted inside the abdominal portion of the esophagus;

FIGS. 3A-D illustrate embodiments of an IMD according to the presentinvention;

FIG. 4 is a block diagram of an IMD for use in an embodiment of thepresent invention, and an external unit for communication andprogramming of the IMD;

FIGS. 5A-B illustrate embodiments of implantable medical devicesaccording to the present invention;

FIG. 6 illustrates an embodiment of an IMD according to the presentinvention;

FIG. 7 is a schematic view of an IMD and a programming system that maybe used in conjunction with embodiments of the IMD; and implantablemedical device according to the present invention;

FIGS. 8A-D illustrate an embodiment of a method of non-surgicallyimplanting an IMD for providing trans-esophageal VNS to a patient totreat a medical condition.

NOTATION AND NOMENCLATURE

Certain terms are used throughout the following description and claimsto refer to particular system components. This document does not intendto distinguish between components that differ in name but not function.In the following discussion and in the claims, the terms “including” and“comprising” are used in an open-ended fashion, and thus should beinterpreted to mean “including, but not limited to . . . ”. Also, theterm “couple” or “couples” is intended to mean either an indirect ordirect electrical connection. Thus, if a first device couples to asecond device, that connection may be through a direct electricalconnection, or through an indirect electrical connection via otherdevices and connections.

The term “implantable medical device” refers to any medical deviceplaced inside the human body. The placement of such a device may occurin a body lumen of the patient, such as the esophagus or a blood vessel,or may involve surgical implantation, such as when a conventional VNSsystem is implanted in the patient's chest and neck area. Furthermore,as defined herein, the term “non-surgical” is used to describe methodsthat do not require incision or dissection of body tissues to effectimplantation of an IMD. In one embodiment, non-surgical implantation mayinvolve placing a medical device in the esophagus of a patient using,e.g., laparoscopic instruments extending from the patient's mouth,through the throat, and into the esophagus.

A “therapeutic signal” refers to a stimulation signal delivered to apatient's body with the intent of treating a medical condition byproviding a modulating effect to neural tissue. “Stimulate” or“stimulation signal” refers to the application of an electrical,mechanical, magnetic, electro-magnetic, photonic, audio and/or chemicalsignal to a neural structure in the patient's body. The signal is anexogenous signal that is distinct from the endogenous electrical,mechanical, and chemical activity (e.g., afferent and/or efferentelectrical action potentials) generated by the patient's body andenvironment. In other words, the stimulation signal (whether electrical,mechanical, magnetic, electro-magnetic, photonic, audio or chemical innature) applied to the nerve in the present invention is a signalapplied from an artificial source, e.g., a neurostimulator.

The effect of a stimulation signal on neural activity is termed“modulation”; however, for simplicity, the terms “stimulating” and“modulating”, and variants thereof, may be used interchangeably. Ingeneral, the application of an exogenous signal to a nerve refers to“stimulation” of the neural structure, while the effects of that signal,if any, on the electrical activity of the neural structure are properlyreferred to as “modulation.”

As defined herein, the term “ambulatory” may describe implantablemedical devices, portions of which a patient may carry around withminimal effect or interruption to his or her daily lifestyle.

In some medical devices, electrical neurostimulation may be provided byimplanting an electrical device (e.g., a pulse generator) underneath theskin of a patient and delivering an electrical signal to a nerve such asa cranial nerve. In one embodiment, the electrical neurostimulationinvolves sensing or detecting a body parameter, with the electricalsignal being delivered in response to the sensed body parameter. Thistype of stimulation is generally referred to as “active,” “feedback,” or“triggered” stimulation. In another embodiment, the system may operatewithout sensing or detecting a body parameter once the patient has beendiagnosed with a medical condition that may be treated byneurostimulation. In this case, the system may apply a series ofelectrical pulses to the nerve (e.g., a cranial nerve such as a vagusnerve) periodically, intermittently, or continuously throughout the day,or over another predetermined time interval. This type of stimulation isgenerally referred to as “passive,” “non-feedback,” or “prophylactic,”stimulation. The electrical signal may be applied by an IMD that isimplanted within the patient's body. In other cases, the signal may begenerated by an external pulse generator outside the patient's body,coupled by an RF or wireless link to an implanted electrode.

Generally, neurostimulation signals that perform neuromodulation aredelivered by the IMD via one or more leads. The leads generallyterminate at their distal ends in one or more electrodes, and theelectrodes, in turn, are electrically coupled to tissue in the patient'sbody. For example, a number of electrodes may be attached to variouspoints of a nerve or other tissue inside a human body for delivery of aneurostimulation signal. In some types of neurostimulation devices,electrodes are coupled to the electrical signal generator without theuse of leads. In the present invention, some embodiments include leadsand some embodiments do not incorporate leads.

While feedback stimulation schemes have been proposed, conventionalvagus nerve stimulation (VNS) usually involves non-feedback stimulationcharacterized by a number of parameters. Specifically, convention vagusnerve stimulation usually involves a series of electrical pulses inbursts defined by an “on-time” and an “off-time.” During the on-time,electrical pulses of a defined electrical current (e.g., 0.5-2.0milliamps) and pulse width (e.g., 0.25-1.0 milliseconds) are deliveredat a defined frequency (e.g., 20-30 Hz) for the on-time duration,usually a specific number of seconds, e.g., 10-100 seconds. The pulsebursts are separated from one another by the off-time, (e.g., 30seconds-5 minutes) in which no electrical signal is applied to thenerve. The on-time and off-time parameters together define a duty cycle,which is the ratio of the on-time to the combination of the on-time andoff-time, and which describes the percentage of time that the electricalsignal is applied to the nerve.

In conventional VNS, the on-time and off-time may be programmed todefine an intermittent pattern in which a repeating series of electricalpulse bursts are generated and applied to the vagus nerve. Each sequenceof pulses during an on-time may be referred to as a “pulse burst.” Theburst is followed by the off-time period in which no signals are appliedto the nerve. The off-time is provided to allow the nerve to recoverfrom the stimulation of the pulse burst, and to conserve power. If theoff-time is set at zero, the electrical signal in conventional VNS mayprovide continuous stimulation to the vagus nerve. Alternatively, theidle time may be as long as one day or more, in which case the pulsebursts are provided only once per day or at even longer intervals.Typically, however, the ratio of “off-time” to “on-time” may range fromabout 0.5 to about 10.

In addition to the on-time and off-time, the other parameters definingthe electrical signal in conventional VNS may be programmed over a rangeof values. The pulse width for the pulses in a pulse burst ofconventional VNS may be set to a value not greater than about 1 msec,such as about 250-500 μsec, and the number of pulses in a pulse burst istypically set by programming a frequency in a range of about 20-150 Hz(i.e., 20 pulses per second to 150 pulses per second). A non-uniformfrequency may also be used. Frequency may be altered during a pulseburst by either a frequency sweep from a low frequency to a highfrequency, or vice versa. Alternatively, the timing between adjacentindividual signals within a burst may be randomly changed such that twoadjacent signals may be generated at any frequency within a range offrequencies.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The disclosed systems, devices and methods are susceptible toimplementation in various embodiments. The disclosure of specificembodiments, including preferred embodiments, is not intended to limitthe scope of the invention as claimed unless expressly specified. Inaddition, persons skilled in the art will understand that the inventionhas broad application. Accordingly, the discussion of particularembodiments is meant only to be exemplary, and does not imply that thescope of the disclosure, including the claims, is limited tospecifically disclosed embodiments.

In some embodiments of the present invention, an implantable medicaldevice may be implanted within a patient's body without surgery. The IMDgenerates and applies an electrical signal to the vagus nerve of thepatient to treat a medical condition. The invention is possible becauseof the unique anatomy of the left and right vagus nerves. From the neckregion, the left vagus nerve rotates anteriorly and becomes attached tothe exterior surface of the abdominal or lower esophagus (i.e. theabdominal portion of the esophagus) as the anterior vagus nerve. As usedherein, “abdominal esophagus” and “lower esophagus” may be usedinterchangeably to refer to the portion of the esophagus running fromthe thorax to the esophagogastric junction of a patient. The right vagusnerve, on the other hand, rotates posteriorly and becomes attached tothe exterior surface of the lower esophagus as the posterior vagusnerve. As the anterior and posterior vagus nerves travel down theesophagus, the nerves separate into a number of branches at theesophagus/stomach junction, and the branches remain attached to theouter wall of the stomach. The close proximity of the nerves to thesurfaces of the abdominal esophagus and the stomach permit theapplication of an electrical signal to the vagus nerve from the interiorof the abdominal esophagus using a medical device coupled to theesophagus's interior wall.

In alternative embodiments, the invention may include devices andmethods for providing electrical signal therapy across the wall of theupper portion of the stomach rather than the abdominal portion of theesophagus. However, the greater accessibility of the vagus nerves at thelower esophagus/stomach junction makes delivery of the signal across thewall of the lower esophagus a preferred embodiment. Application of atherapeutic electrical signal to the stomach is more difficult than theesophagus for a number of reasons. First, the motility of the esophagusis less than that of the stomach, thus making the esophagus a morestable structure. Second, the anterior and posterior vagus nerves areessentially a unitary structure (i.e., a single nerve bundle—albeit withthousands of individual nerve fibers within it—traveling down the lengthof the lower esophagus), with limited branching until passing onto thesurface of the stomach. Accordingly, stimulation of the vagus at thelower esophagus level facilitates modulation of a larger population ofnerves than stimulation of only some of the vagus nerve branches on theupper portion of the stomach.

In one embodiment, an ambulatory implantable medical device may benon-surgically implanted within the abdominal esophagus of a patient todeliver an electrical signal to at least one of the anterior orposterior vagus nerves through the wall of the esophagus.

FIGS. 1 and 2 depict an IMD 100 implanted in a patient. In oneembodiment, IMD 100 comprises a support member 101. Support member 101comprises a flexible, biocompatible material and is adapted to becoupled to the inner wall of the lower esophagus of the patient.Moreover, support member 101 has one or more electrodes 103 coupled toits outer surface. An electrical signal generator 122 generates atherapeutic electrical signal to apply to the vagus nerve 133. Signalgenerator 122 is electrically coupled to electrodes 103. In someembodiments, the electrodes 103 are coupled to the electrical signalgenerator 122 by leads, while in alternative embodiments the electrodesare directly connected to the electrical signal generator without theuse of leads. In addition, programming system 120 may be coupled toelectrical signal generator 122. Programming system 120 may generallycontrol and monitor IMD 100 from outside the body as IMD 100 providesstimulation to the vagus nerve to provide therapy to a patient.

In one embodiment, the support member 101 has at least one unipolarelectrode coupled to its outer surface. In another embodiment, thesupport member 101 has a plurality of unipolar electrodes on its outersurface. The plurality of electrodes may include a first plurality on afirst side of the support member 101, and a second plurality on a secondside of the support member 101. The first plurality may be adapted toprovide a trans-esophageal therapeutic electrical signal to an anteriorvagus nerve of the patient, and the second plurality of electrodes maybe adapted to provide a trans-esophageal therapeutic electrical signal(which may be the same as or different from the signal provided by thefirst plurality) to a posterior vagus nerve of the patient. Electrodes103 are used to apply an electrical signal to the vagus nerve 133through the wall of the lower esophagus 131. In one embodiment, theelectrodes 103 contact or engage the inner wall of the esophagus 131. Inanother embodiment, the electrodes are adapted to partially penetratethe wall of the lower esophagus 131. In a still further embodiment, theelectrodes are adapted to completely penetrate the wall of the loweresophagus 131, and in yet another embodiment, the electrodes maycomprise multiple electrode elements, some of which contact the innerwall of the esophagus, some of which partially penetrate the esophaguswall, and some of which completely penetrate the wall. Without beingbound by theory, it is believed that greater penetration of the wall ofthe esophagus corresponds with more efficient stimulation of the vagusnerve on the outer wall of the esophagus, since the signal fromelectrode penetrating the wall in whole or in part will be lessattenuated than a signal from electrodes that contact the inner wall ofthe esophagus without penetration of the same.

In one embodiment, support member 101 has at least one electrode pair(e.g., a cathode and an anode) coupled to its outer surface. In anotherembodiment, support member 101 has a plurality of electrode pairs on itsouter surface. In a further embodiment, support member 101 has at leastone unipolar electrode as well as at least one electrode pair on itsouter surface. In general, the disposition of electrodes (whetherunipolar, bipolar, or a combination of unipolar and bipolar electrodes)may be used to steer the electrical current of the therapeuticelectrical signal to effectively modulate the anterior and/or posteriorvagus nerves of the patient.

IMD 100 is preferably implanted non-surgically, as described below inmore detail. However, in general, IMD 100 is implanted in the lower orabdominal portion of the esophagus via oral insertion of the IMD 100through the patient's mouth and passage through the throat and the upperesophagus. Since IMD 100 is implanted within the lower esophagus, noincisions are necessary to position the IMD 100 at the desiredimplantation site. The IMD 100 may be retained in place and migrationprevented by suitable anchors to engage the tissue of the esophagus 131.The anchors may comprise any of a number of medical anchors known in theart, e.g., sutures, barbs, staples, adhesives, pins, etc. The IMD 100may further comprise a retainment element to facilitate maintaining thedevice in position in the esophagus and to prevent migration. In oneembodiment, the support member 101 comprises a ring or partial ringstructure with a retainment element comprising a resilient spring madeof metal or other suitable material. The resilient spring may beembedded in or coupled to support member 101 (e.g., by mechanicalaffixation). Support member 101 ring or partial ring may be sized to beslightly larger than the diameter of the patient's esophagus, such thatthe resilient spring retainment element coupled thereto provides aradially outwardly directed force against the lower esophagus tomaintain the device in a fixed position in the esophagus, while allowingthe IMD 100 to flex with normal movement of the esophagus.

Once implanted, IMD 100 provides therapy to the patient by generatingand applying an electrical signal to the vagus nerve across the wall ofthe esophagus 131. As used herein, the terms “trans-esophageal” or“trans-esophageally” refer to or describe delivery of a therapy (i.e.vagus nerve stimulation) across the esophageal wall. The signalpreferably comprises an electronic signal generated by the electronicsignal generator 122 in the inner lumen of the esophagus and appliedtrans-esophageally to the vagus nerve on the outer surface of theesophagus wall. The electrical signal provided by the electronic signalgenerator 122 may be defined by programming system 120. In someembodiments, the patient may control and/or alter the therapy by a usersignal, e.g., a magnet, a tap sensor, or a patient module fornoninvasively transmitting and/or receiving data from the IMD 100, e.g.,by RF signals.

Generally, as mentioned above, neurostimulation signals that performneuromodulation are delivered by the IMD 100 via one or more electrodes103 as shown in FIG. 2. The modulating effect of the neurostimulationsignal upon the neural tissue may be excitatory or inhibitory, and maypotentiate acute and/or long-term changes in neuronal activity. Forexample, the “modulating” effect of the stimulation signal to the neuraltissue may comprise one more of the following effects: (a) initiation ofan action potential (afferent and/or efferent action potentials); (b)inhibition or blocking of the conduction of action potentials, whetherendogenous or exogenously induced, including hyperpolarizing and/orcollision blocking, (c) affecting changes inneurotransmitter/neuromodulator release or uptake, and (d) changes inneuro-plasticity or neurogenesis of brain tissue.

In a preferred embodiment, the support member 101 is a ring-shaped ortube-shaped member defining a circular cross-section as shown in FIG. 3.The diameter of the support member 101 may be sized to match or slightlyexceed the diameter of the esophagus 131. Alternatively, support member101 may be semi-circular, i.e., comprising an incomplete circle or aC-shape as shown in FIG. 5B. More generally, support member 102 may beof any suitable geometry that conforms to at least a portion of theinner surface of an organ.

Referring to FIG. 5A, in one embodiment, the support member 101comprises a generally planar, flexible member that is capable of bendingto conform to a portion of the inner wall of the lower esophagus 131. Insuch an embodiment, support member 101 may be comprised of abiocompatible polymer such as silicone rubber in a suitable shape, i.e.,a circular shape, a rectangular shape, or any desired shape, and mayhave an electrical signal generator 122 coupled thereto (for example byembedding the electrical signal generator in the biocompatible polymer).Furthermore, in such an embodiment, support member 101 may be attachedto inner wall of esophagus by using a tissue adhesive or biocompatibleglue.

In another embodiment, the support member may include a retainmentelement comprising an expandable stent, which may be introduced into thelumen of the esophagus 131 in a compressed state via conventionalballoon catheters, and then expanded by inflating the balloon to conformthe device to the size of the esophagus.

According to another embodiment of the invention, the support member 101has a contracted position to facilitate introduction and implantation ofthe device in the esophagus, and an expanded position engaging the innerwall of the esophagus to maintain the device in position and reduce oreliminate migration. In one aspect, the support member 101 has a fixedexpanded position to hold the device in place within the esophagus. Asdescribed in detail above, support member 101 may comprise a retainmentelement that may be a resilient spring member or a stent to provide aradially outwardly directed force against the inner wall of theesophagus. In addition, support member 101 and the retainment elementmay be mounted on a catheter in the first, contracted position tofacilitate introduction of the IMD 100 into the patient's mouth andpassage through the upper esophagus into the lower esophagus, whereuponthe IMD 100 may be deployed in the expanded position and optionallyfurther retained in position with one or more anchor members.

In one embodiment, support member 101 may further comprise one or moreanchor members (not shown) for attaching the IMD 100 to the inner wallof the esophagus 131. For example, support member 101 may comprise aplurality of suture elements such as a suture ring or apertures so thata surgeon may suture the IMD 100 to the inner esophageal wall to preventdisplacement of the IMD 100. In another aspect, the anchor members maycomprise a plurality of barbs or protrusions which are capable ofgrasping or engaging the inner surface of the esophagus, and/or ofpenetrating the wall of the esophagus, to prevent movement ordisplacement. The barbs or protrusions may be disposed in closeproximity to the electrodes 103 so as to stabilize the IMD 100 in afixed position relative to the anterior and/or posterior vagus nerves.In a further embodiment, the electrodes 103 may serve as anchor members.For example, electrodes 103 themselves may comprise protrusions whichproject radially from the support member 101 to engage the wall of theesophagus 131. The electrodes 103 may contact the inner surface of theesophagus wall, and/or may comprise barbs to penetrate the wall in wholeor part. Another means of engaging the inner wall of the esophaguscomprises a tissue adhesive or biocompatible glue coated on to the outersurface of support member 101.

The support member 101 may be made of any suitable biocompatiblematerial. The materials used in fabricating the IMD 100 are preferablynon-toxic such that if the IMD 100 is dislodged into the stomach, it mayeasily pass through the digestive system. In a preferred embodiment,support member 101 is made of a resilient or flexible biocompatiblematerial such as a polymer. Suitable polymers include withoutlimitation, hydrogels, silicone, polyethylene, polypropylene,polyurethane, polycaprolactone, polytetrafluoroethylene (PTFE),copolymers and combinations of the foregoing, and the like. In anotherembodiment, the support member is made of a silicone polymer. Inalternative embodiments, support member 101 is made of biocompatiblemetals such as without limitation, titanium, silver, gold, alloys,nitinol, shape-memory metals, or combinations thereof. Furthermore,support member 101 may be made of biological materials such astissue-engineered esophageal tissue from an animal donor, bovinepericardium, and the like. Where human or animal tissue from a donor isused, the materials are preferably decellularized and cross-linked tominimize adverse immunological reactions and prevent the immune systemof the patient from degrading the materials.

FIG. 6 illustrates an embodiment of an IMD 100. IMD 100 may comprise aretainment element 142 comprising a skeleton or frame embedded within asupport member 101. The support member may in some embodiments comprisea polymer exterior or coating 144 (e.g., a fabric exterior or engineeredpolymer to provide improved biocompatibility). The retainment element142 (depicted in a grid-like configuration although many othergeometries may be employed) may be made of a flexible metal or polymer,and has sufficient stiffness when support member 101 is in an expandedposition to maintain the position of the IMD 100 in the esophagus. Thesupport member 101 serves as a substrate to which to mount theelectrodes 103 and other components of the IMD 100 (e.g., a pulsegenerator and a controller). In a specific embodiment, theexterior/coating 144 comprises a fatty acid derivative covalently bondedto a silicone polymer comprising the support member 101.

According to an embodiment, when the support member 101 and theretainment element 142 are expanded, they typically have a diameter orsize that corresponds to the inner dimensions of the esophagus. Forexample, the esophagus has an inner diameter ranging from approximately10 mm to approximately 30 mm. As such, in an embodiment, the supportmember 101 has an expanded size ranging from approximately 8 mm to about50 mm, preferably from about 10 mm to about 40 mm, more preferably fromabout 10 mm to about 35 mm in diameter. In other embodiments, differentsupport members 101 may be fabricated with different sizes such that asurgeon may have the option of selecting the most appropriate sizedepending on the patient.

The exterior or outer surface of the support member 101 comprises one ormore electrodes 103 which apply a therapeutic electrical signal to thewall of the lower esophagus 131. As noted, in alternative embodimentsthe electrodes 103 may provide an electrical signal therapy across thewall of the upper portion of the stomach instead of or in addition tothe lower portion of the esophagus. At any rate, electrodes 103 aredisposed on support member 101 such that they will be in close proximityto the vagus nerve when the IMD 100 is non-surgically implanted in theesophagus. Preferably, the electrodes comprise a conductive materialsuch as platinum, iridium, platinum-iridium alloys, gold, silver,copper, aluminum, and/or oxides of the foregoing. The electrodes 103 maybe arranged in any suitable pattern on the exterior of the ring. Thepattern is preferably optimized to deliver electrical stimulation to theanterior and/or posterior vagus nerves regardless of the location of theIMD 100 within the esophagus. According to one embodiment, electrodes103 are arranged as parallel bands or rings around all or part of theouter surface of the IMD 100 as shown in FIG. 3A. In another embodiment,electrodes 103 are arranged as rows of circular or hemisphericalcontacts as shown in FIGS. 3B and 3D, respectively. In still anotherembodiment, electrodes 103 are arranged in vertical columns ofelectrodes, with each column acting as a unipolar electrode, a cathodeor an anode (FIG. 3C). FIG. 3D also depicts other components of the IMD100 embedded in support member 101, including a power supply 430, asignal generation unit 420, and a controller 410, as more fullydiscussed with regard to FIG. 4, below. In some embodiments, apertures104 may be provided as shown in FIG. 3D for use in conjunction with ananchor member (not shown) such as a suture, barb, pin, etc. This mayfacilitate modulation of the vagus nerve if rows of electrodes areplaced on either side of the descending vagus nerve bundle(s).

FIG. 4 illustrates a block diagram depiction of the IMD 400 of FIG. 1,in accordance with one illustrative embodiment of the present invention.The IMD 400 may be used for electrical signal therapy to treat variousdisorders, such as (without limitation) epilepsy, depression, bulimia,heart rhythm disorders, gastric-related disorder, a hormonal disorder, areproductive disorder, a metabolic disorder, a hearing disorder, and/ora pain disorder. The IMD 400 may be coupled to various leads, ifnecessary, and one or more electrodes for applying a therapeuticelectrical signal to an anterior and/or posterior vagus nerve of thepatient. Therapeutic electrical signals may be transmitted from the IMD400 to a lower esophagus wall of the patient, and across the wall of theesophagus to the patient. The electrodes may be positioned either incontact with the inner wall of the esophagus, or may penetrate the wallof the esophagus in whole or in part. The net effect of the IMD 400 andthe electrodes is to generate an electrical signal in the inner lumen ofthe esophagus and to transmit that signal from the inner lumen to avagus nerve located outside the wall of the esophagus. Therapeuticelectrical signals from the IMD 400 may be generated by a signalgeneration unit 420 and transmitted to the electrode(s) either directlyor via one or more leads (not shown). Further, signals from sensorelectrodes, which may also have corresponding leads, may also be coupledto the IMD 400. In one embodiment, the electrodes applying the signal tothe vagus nerve may also function as sensing electrodes. Sensingelectrodes may be used to trigger feedback stimulation routines basedupon, e.g., body temperature, EEG recordings, heart rate, vagus nerveactivity, etc.

The IMD 400 may comprise a controller 410 capable of controlling variousaspects of the operation of the IMD 400. The controller 410 is capableof receiving internal data and/or external data and controlling thegeneration and delivery of a therapeutic electrical signal to a vagusnerve of the patient's body. For example, the controller 410 may receivemanual instructions from an operator externally, or may generate andapply a therapeutic electrical signal based on internal calculations andprogramming. The controller 410 is capable of affecting substantiallyall functions of the IMD 400.

The controller 410 may comprise various components, such as a processor415, a memory 417, etc. The processor 415 may comprise one or moremicrocontrollers, microprocessors, etc., that are capable of executing avariety of software components. The memory 417 may comprise variousmemory portions, where a number of types of data (e.g., internal data,external data instructions, software codes, status data, diagnosticdata, etc.) may be stored. The memory 417 may store various tables orother database content that could be used by the IMD 400 to implementthe override of normal operations. The memory 417 may comprise randomaccess memory (RAM) dynamic random access memory (DRAM), electricallyerasable programmable read-only memory (EEPROM), flash memory, etc.

The IMD 400 may also comprise a signal generation unit or pulsegenerator 420. The signal generation unit 420 is capable of generatingand delivering a variety of electrical neurostimulation signals to oneor more electrodes, e.g., via leads. The signal generation unit 420 iscapable of generating a therapy portion, a ramping-up portion, and aramping-down portion of the therapeutic electrical signal. In oneembodiment, a number of leads may be used to electrically couple the oneor more electrodes to the IMD 400. In another embodiment, the electrodesmay be directly coupled to the signal generation unit 420. Thetherapeutic electrical signal may be delivered to the electrodes by thesignal generation unit 420 based upon instructions from the controller410. The signal generation unit 420 may comprise various types ofcircuitry, such as pulse generators, impedance control circuitry tocontrol the impedance “seen” by the leads, and other circuitry thatreceives instructions relating to the type of electrical signal therapyto be provided to the patient. The signal generation unit 420 is capableof delivering a controlled current therapeutic electrical signal to theelectrodes.

The IMD 400 may also comprise a power supply 430. The power supply 430may comprise a battery, voltage regulators, capacitors, etc., to providepower for the operation of the IMD 400, including delivering thetherapeutic electrical signal. The power supply 430 provides power forthe operation of the IMD 400, including electronic operations and theelectrical signal function. The power supply is typically a battery. Thepower supply 430 may comprise a lithium/thionyl chloride cell or alithium/carbon monofluoride cell. Other battery types known in the artof implantable medical devices may also be used. Any suitable batteriesmay be used including without limitation, lithium ion, nickel cadmiumalkaline, and the like. In a preferred embodiment, the power supplycomprises a battery located inside support member 401 and coupled to thepulse generator 420. In an alternative embodiment, the power supply isrechargeable. In one aspect, the power supply may be wirelesslyrechargeable. A wirelessly rechargeable power supply may include anexternal power supply on the outside of the patient's body, inductivelycoupled to an implanted rectifier and/or capacitor attached to thesupport member 401. Such a power supply may be charged from outside thepatient's body without requiring removal of the medical device. In analternative embodiment, the power supply 430 may comprise a powerconverter to convert energy from the patient's body into electricalpower for the IMD 400. The converter may use a temperature differencewithin the patient's body or between the patient's body and theenvironment to generate electrical power, or may convert body movement(e.g., gastric motility movement, arm movement, or leg movement) intoelectrical energy to provide power to the IMD 400. In anotherembodiment, an external power supply may be part of an external unit 120as will be described below.

The IMD 400 also comprises a communication unit 460 capable offacilitating communications between the IMD 400 and various devices. Inparticular, the communication unit 460 is capable of providingtransmission and reception of electronic signals to and from an externalunit 120. In particular, communication unit 460 may be a wireless devicecapable of transmitting and receiving signals to and from IMD 400without the use of wires. In some embodiments, the controller 410 andsignal generator 420 may be part of an external unit or programmingsystem 120, described in more detail below.

The external unit 120 may be a device that is capable of programmingvarious modules and electrical signal parameters of the IMD 400. In oneembodiment, the external unit 120 comprises a computer system that iscapable of executing a data-acquisition program. The external unit 120may be controlled by a healthcare provider, such as a physician, at abase station in, for example, a doctor's office. The external unit 120may be a computer, preferably a handheld computer or PDA, but mayalternatively comprise any other device that is capable of electroniccommunications and programming. The external unit 120 may downloadvarious parameters and program software into the IMD 400 for programmingthe operation of the implantable device. The external unit 120 may alsoreceive and upload various status conditions and other data from the IMD400. The communication unit 460 may be hardware, software, firmware,and/or any combination thereof. Communications between the external unit120 and the communication unit 460 may occur via a wireless or othertype of communication, illustrated generally by line 475 in FIG. 4.

The IMD 400 is capable of delivering a therapeutic electrical signalthat can be intermittent, periodic, random, sequential, coded, and/orpatterned. The electrical signals may comprise an electrical signalfrequency of approximately 0.1 to 1000 Hz. The electrical signals maycomprise a pulse width of in the range of approximately 1-2000microseconds. The electrical signals may comprise current amplitude inthe range of approximately 0.1 mA to 10 mA. The therapeutic electricalsignal may be delivered through either bipolar electrodes (i.e., acathode (−) electrode and an anode (+) electrode), or may be deliveredthrough one or more unipolar electrodes. In one embodiment, the variousblocks illustrated in FIG. 4 may comprise a software unit, a firmwareunit, a hardware unit, and/or any combination thereof.

The IMD 400 may also comprise a magnetic field detection unit 490. Themagnetic field detection unit 490 is capable of detecting magneticand/or electromagnetic fields of a predetermined magnitude. Whether themagnetic field results from a magnet placed proximate to the IMD 400, orwhether it results from a substantial magnetic field encompassing anarea (such as an MRI machine), the magnetic field detection unit 490 iscapable of informing the IMD of the existence of a magnetic field.

The magnetic field detection unit 490 may comprise various sensors, suchas a Reed Switch circuitry, a Hall Effect sensor circuitry, and/or thelike. The magnetic field detection unit 490 may also comprise variousregisters and/or data transceiver circuits that are capable of sendingsignals that are indicative of various magnetic fields, the time periodof such fields, etc. In this manner, the magnetic field detection unit490 is capable of deciphering whether the detected magnetic fieldrelates to an inhibitory input or an excitatory input from an externalsource. The inhibitory input may refer to inhibition of, or deviationfrom, normal signal generation operation. The excitatory input may referto additional electrical signal therapy or deviation from normalelectrical signal therapy.

The IMD 400 may also include an electrical signal override unit 480. Theelectrical signal override unit 480 is capable of overriding thereaction by the IMD to the detection of a magnetic signal provided bythe magnetic field detection unit 490. The electrical signal overrideunit 480 may comprise various software, hardware, and/or firmware unitsthat are capable of determining an amount of time period in which tooverride the detection of a magnetic field. The signal override unit 480may also contain safety features, such as returning to normal operationdespite an override command after a predetermined period of time. Theelectrical signal override unit 480 is capable of preventing falseinterruption of normal operation due to false magnetic input signals orunintended magnetic input signals. The override unit 480 may receive anexternal indication via the communication unit 460 to engage in anoverride mode for a predetermined period of time.

In an embodiment, components of IMD 400 (i.e. controller 410, signalgeneration unit 420, etc.) are all coupled to support member 401 asdescribed in detail above. Furthermore, support member 401 andcomponents of IMD 400 may be completely integrated into a compact andunitary device. That is, each component of IMD 400 may be integral tothe support member 401. Thus, in such embodiments, the IMD 400 may be acomplete standalone device without the need for any external devices tobe carried around by a patient. As such, one of the many advantages ofthe IMD is that it may allow a patient to be completely ambulatory whenthe IMD is implanted, and providing maximum quality of life to thepatient.

It is also contemplated that various embodiments of the IMD may betemporary or permanent. That is, in some embodiments, IMD may beconstructed to be inexpensive and easily disposable. For example, inparticular embodiments, the IMD may be designed to be replaced once thepower supply has been consumed. Such devices may be resident in the bodyof the patient for from several months up to several years, althoughshorter or longer residence times are possible. In other embodiments,IMD may be designed for permanent or long term operation such it willnot need replacement for time periods of 10 years or more. Anotheradvantage of the device is that it is easily removable.

FIGS. 2 and 7 illustrate an external unit or programming system 120comprising a programming device 124 coupled to a wand 128 fortransmitting and receiving signals to and from the IMD 100. As mentionedabove with respect to FIG. 4, the IMD 100 preferably comprises a signalor pulse generator 122, and a controller to control the generation anddelivery of the electrical signal by the pulse generator 122. Thecontroller preferably is, or includes a central processing unit (CPU)such as a low-power, mixed-signal microcontroller. In alternativeembodiments, the controller and pulse generator 122 may be part of anexternal programming system 120, described in more detail below.

In an additional embodiment, the IMD 100 comprises a power supply whichis coupled to the support member 101, and to the pulse generator 102.The power supply is typically a battery, such as a lithium carbonmonofluoride (LiCFx), lithium ion, nickel cadmium alkaline, and thelike. In a preferred embodiment, the power supply comprises a batterylocated inside support member 101 and coupled to the pulse generator102. In an alternative embodiment, the power supply is rechargeable. Inone aspect, the power supply may be wirelessly rechargeable. Awirelessly rechargeable power supply may include an external powersupply on the outside of the patient's body, inductively coupled to animplanted rectifier and/or capacitor attached to the support member 101.Such a power supply may be charged from outside the patient's bodywithout requiring removal of the medical device. In another embodiment,an external power supply may be part of an external programming system120 as will be described below.

FIGS. 2 and 7 further illustrate a programming system 120 comprising aprogramming device 124 coupled to a wand 128, for transmitting andreceiving wireless signals (e.g., RF signals) to and from the IMD 100.The programming device 124 may comprise a personal computer, personaldigital assistant (PDA) device, or other suitable computing deviceconsistent with the description contained herein. Methods and apparatusfor communication between an IMD 100 and an external programming system120 are known in the art. In one embodiment, the IMD 100 includes atransceiver (such as a coil) that permits signals to be communicatedwirelessly and non-invasively between the programming device 124 (viathe external wand 128) and the implanted IMD 100. Wand 128 facilitateswireless communication and may be placed on the skin of the patient'sbody overlying the implant site of the IMD 100. The programming system120 may also monitor the performance of the IMD 100 and download newprogramming parameters to define the therapeutic electrical signal(e.g., on-time, off-time, pulse width, current amplitude, frequency)into the IMD 100 to alter its operation as desired. In variousembodiments, portions of the programming system may be integrated intothe IMD 100, itself, or may be external to the IMD 100.

FIG. 7 shows a block diagram of one embodiment of the programming system120. As shown, the programming system 120 is external to the patient'sbody, and includes the programming device 124 and the wand 128.Programming system 120 generally assists, controls, and/or programs theIMD 100 and may also receive data from the IMD referring to status andoperational conditions stored in or generated by the IMD, such asbattery and lead diagnostic information, remaining battery lifecalculations, current programming parameters, patient identificationinformation, programming history information, etc. Thus, in anembodiment, the IMD 100 generates a therapeutic pulsed electrical signalfor application to the vagus nerve 133 in a patient under the control ofprogramming system 120.

Programming device 124 preferably includes a central processing unit(CPU) 236 such as a low-power, mixed-signal microcontroller. In general,any suitable processor can be used to implement the functionalityperformed by the programming device 124 as explained herein. It will beappreciated that some features of the programming system 120 may also beprovided in whole, or in part, by the IMD 100, and vice versa. Thus,while certain features of the present invention may be described as partof the IMD 100, it is not intended thereby to preclude embodiments inwhich the features are provided by the programming system 120. Likewise,describing certain features herein as part of the programming system 120does not preclude embodiments in which the features are included as partof the IMD 100.

The CPU 236 of programming device 124 is preferably coupled to a memory250. The memory 250 may comprise volatile (e.g., random access memory)and/or non-volatile memory (e.g., read only memory (ROM),electrically-erasable programmable ROM (EEPROM), Flash memory, etc.).Memory 250 may comprise any suitable storage medium. Examples ofsuitable storage media include without limitation, USB flash drives,Compact Flash cards, memory sticks, Smart Media cards, Secure Digital(SD) cards, xD cards, CD-ROM, DVD-ROM, tape drives, Zip disks, floppydisk, RAM, hard drives, etc. The memory 250 may be used to store code(e.g., diagnostic software) that is executed by the CPU 236. Theexecutable code may be executed directly from the non-volatile memory orcopied to a volatile memory for execution therefrom.

In addition, programming device 124 of programming system 120 may have adisplay or output 232 such that a user may monitor the functions orproperties of the IMD 100. In some embodiments, programming system 120may have a graphical user interface. In preferred embodiments, a usermay input parameter settings using an input device 238 through thegraphical user interface on the display 232, or other input means.Memory 250 may store data received from the IMD 100 or may be used tostore software 380 (e.g., diagnostic software, therapy programs, code,etc.) that is executed by the CPU 236. The executable code may beexecuted directly from the non-volatile memory or copied to the volatilememory for execution therefrom.

In one embodiment, the programming system 120 may be used by a physicianas part of an office computer system, in which the IMD 100 is queriedregularly during office visits by the patient. According to anotherembodiment, programming system 120 may be ambulatory, and wand 128 maybe continuously in contact with the patient's skin near implant site(i.e., the abdominal region) to provide continuous control of IMD 100 inconjunction with a portable handheld device 124 that may comprise, e.g.,a PDA. Wand 128 is coupled to the programming device 124 which may beconveniently worn by the patient on a belt, pocket, and the like. Inanother embodiment, programming device 124 and wand 128 are integratedinto a single device which is kept in continuous proximity to the IMD100 so as to maintain wireless communication with the IMD 100 throughthe skin.

In an embodiment of a method of providing an electrical signal to avagus nerve, an IMD 100, as described in detail above, is implanted inthe esophagus 131 of a patient. See FIGS. 8A-D. In at least oneembodiment, the IMD 100 is implanted in the lower or abdominal portionof the esophagus 131 at or below the patient's diaphragm, e.g., wherethe anterior and posterior vagus nerves are attached to the exteriorwall of the esophagus 131 near the esophagogastric junction. Preferably,the IMD 100 is delivered to the implantation site in the esophagus 131orally i.e. through the mouth and esophagus as shown in FIGS. 8A and 8B.In a particular embodiment, IMD 100 may be implanted via a catheterdelivery system. Specifically, IMD 100 may be mounted at the end of acatheter 210, e.g., at a balloon portion 211 of a balloon catheter inits contracted position. The catheter 210 and IMD 100 may then beinserted into the patient's mouth and throat (i.e. orally), and advancedinto the esophagus as shown in FIG. 8A. Preferably, the catheter 210 isinserted until the distal tip is near the esophagogastric junction(i.e., at the intersection of the esophagus and the stomach) as thisportion of the esophagus 131 is where the vagus nerve 133 reforms fromthe esophageal plexus to form the anterior and posterior vagal trunks.See FIG. 8B.

Once the distal tip of catheter 210 is disposed at the desiredimplantation site for IMD 100, the IMD 100 is deployed (for example, toan expanded position) and anchored to the inner wall of the esophagus.If a balloon catheter is used, the balloon portion may be inflated toexpand the support member 101. A balloon catheter may be used, forexample, in conjunction with a support member comprising a stent orstent-like retainment element. Alternatively, the support member 101 maycomprise a wire or band of a shape-memory metal such as Nitinol or aresilient polymer to provide strength and additional support to thesupport member 101. The support member 101 (with the retainment element)may be wrapped around, folded, compressed or otherwise reduced to acontracted position and retained in position on the catheter by sutures,releasable wires, or other constraining means known in the art, where aconstraint is needed.

Once in position, FIG. 8C, the IMD 100 deployed into place against theinner wall of the esophagus, FIG. 8D by, for example, removing a theconstraining means or expanding a balloon catheter. The IMD 100 may thenbe anchored in place using anchors known in the art, e.g., sutures,barbs, staples, adhesives, pins, etc. In one embodiment, the anchors arethe electrodes, which comprise barbs to engage and penetrate into thewall of the esophagus. In another embodiment, anchors are not used, andthe device may be retained in place solely by a retainment element, suchas a C-shaped spring embedded in the support member 101.

In one embodiment, IMD 100 is implanted such that electrodes 103 are incontact with the inner wall surface of the esophagus 131. Onceimplanted, the IMD 100 provides electrical signal therapy (e.g., vagusnerve stimulation) to a vagus nerve by applying a therapeutic electricalsignal through one or more electrodes 103 to the inner surface of theesophagus wall, through the wall of the esophagus, and to the vagusnerve 133 on the outer surface of the esophagus 131. In anotherembodiment, at least one electrode penetrates into the wall of theesophagus, and the electrical signal is applied to the wall of theesophagus, penetrates the outer wall, and generates action potentials inthe vagus nerve. The electrical signal may be defined an a variety ofways known in the art using a number of different parameters of thesignal such as without limitation, pulse width, current amplitude,frequency, on-off time, duty cycle, number of pulses per burst,interburst period, interpulse interval, burst duration, or combinationsthereof. In general, these parameters may be adjusted through theprogramming system 120.

Vagus nerve stimulation (VNS) may involve non-feedback stimulationcharacterized by a number of parameters. Specifically, vagus nervestimulation may involve a series of electrical pulses in bursts definedby an “on-time” and an “off-time.” During the on-time, electrical pulsesof a defined electrical current (e.g., 0.5-10.0 milliamps) and pulsewidth (e.g., 0.25-1.5 milliseconds) are delivered at a defined frequency(e.g., 20-30 Hz) for the on-time duration, usually a specific number ofseconds, e.g., 7-120 seconds. The pulse bursts are separated from oneanother by the off-time, (e.g., 30 seconds-5 minutes) in which noelectrical signal is applied to the nerve. The on-time and off-timeparameters together define a duty cycle, which is the ratio of theon-time to the combination of the on-time and off-time, and whichdescribes the percentage of time that the electrical signal is appliedto the nerve. In other embodiments, vagus nerve stimulation may comprisea feedback stimulation scheme.

In VNS, the on-time and off-time may be programmed to define anintermittent pattern in which a repeating series of electrical pulsebursts are generated and applied to the vagus nerve. Each sequence ofpulses during an on-time may be referred to as a “pulse burst.” Theburst is followed by the off-time period in which no signals are appliedto the nerve. The off-time is provided to allow the nerve to recoverfrom the stimulation of the pulse burst, and to conserve power. If theoff-time is set at zero, the electrical signal in conventional VNS mayprovide continuous stimulation to the vagus nerve. Typically, however,the ratio of “off-time” to “on-time” may range from about 0.5 to about10.

In addition to the on-time and off-time, the other parameters definingthe electrical signal in conventional VNS may be programmed over a rangeof values. The pulse width for the pulses in a pulse burst ofconventional VNS may be set to a value not greater than about 1 msec,such as about 250-500 μsec, and the number of pulses in a pulse burst istypically set by programming a frequency in a range of about 20-150 Hz(i.e., 20 pulses per second to 150 pulses per second). A non-uniformfrequency may also be used. Frequency may be altered during a pulseburst by either a frequency sweep from a low frequency to a highfrequency, or vice versa. Alternatively, the timing between adjacentindividual signals within a burst may be randomly changed such that twoadjacent signals may be generated at any frequency within a range offrequencies.

Accordingly, the electrical signal may be varied in a number of waysknown in the art using a number of different parameters of the signalsuch as without limitation, pulse width, current amplitude, frequency,on-off time, duty cycle, number of pulses per burst, interburst period,interpulse interval, burst duration, or combinations thereof. Ingeneral, these parameters may be adjusted through the programming system120.

It is envisioned that the disclosed device and methods may have manyapplications associated with vagus nerve stimulation or VNS therapy.Embodiments of the IMD may be used to treat a wide variety of medicalconditions without exposing the patient to surgical complications,including without limitation epilepsy, neuropsychiatric disorders(including but not limited to depression), eating disorders/obesity,traumatic brain injury/coma, addiction disorders, dementia, sleepdisorders, pain, migraine, endocrine/pancreatic disorders (including butnot limited to diabetes), motility disorders, hypertension, congestiveheart failure/cardiac capillary growth, hearing disorders, angina,syncope, vocal cord disorders, thyroid disorders, pulmonary disorders,and reproductive endocrine disorders (including fertility) in a patient.The IMD may be easily deployed and may also avoid undesired sideeffects, in particular voice alteration, by providing a therapeuticelectrical signal to the vagus nerve in a location remote from thelarynx compared to conventional vagus nerve stimulation systemsimplanted in the neck area.

While embodiments of this invention have been shown and described,modifications thereof can be made by one skilled in the art withoutdeparting from the spirit or teaching of this invention. The embodimentsdescribed herein are exemplary only and are not limiting. Manyvariations and modifications of the system and apparatus are possibleand are within the scope of the invention. Accordingly, the scope ofprotection is not limited to the embodiments described herein, but isonly limited by the claims which follow, the scope of which shallinclude all equivalents of the subject matter of the claims.

1. A medical device for providing a therapeutic electrical signal to avagus nerve of a patient comprising: a support member having an outersurface adapted to engage the inner surface of an esophagus; at leastone electrode disposed on the outer surface of said support member, saidat least one electrode adapted to apply a trans-esophageal electricalsignal to a vagus nerve of the patient through the wall of theesophagus, wherein said at least one electrode penetrates the wall ofthe esophagus; one or more anchors to secure said support member to theinner surface of the esophagus, wherein said one or more anchorscomprises said at least one electrode; and a signal generator coupled tothe support member and to the at least one electrode, wherein saidsignal generator generates said electrical signal for application to thevagus nerve.
 2. The medical device of claim 1, wherein said supportmember has a contracted size and an expanded size.
 3. The medical deviceof claim 1, wherein said support member comprises a stent.
 4. Themedical device of claim 1, wherein said support member comprises aplanar, flexible member, a ring member, or a partial ring member.
 5. Themedical device of claim 1, wherein said support member comprises apolymer, a metal, or combinations thereof.
 6. The medical device ofclaim 5, wherein said support member comprises a polymer selected fromthe group consisting of a silicone polymer, a hydrogel, polyethylene,polypropylene, polyurethane, polycaprolactone, polytetrafluoroethylene(PTFE), and combinations thereof.
 7. The medical device of claim 1,further comprising a retainment member coupled to said support member.8. The medical device of claim 7, wherein said retainment member isselected from the group consisting of a stent, a metallic ring, ametallic wire, a metallic mesh, a polymer ring, and a polymer mesh. 9.The medical device of claim 1, further comprising a power supply coupledto said signal generator.
 10. The medical device of claim 1, comprisinga plurality of electrodes.
 11. The medical device of claim 10, whereinsaid plurality of electrodes are a plurality of parallel bands disposedaround the outer surface of said support member.
 12. The medical deviceof claim 1, wherein said one or more anchors comprise sutures, barbs,staples, adhesives, pins, or combinations thereof.
 13. An implantablemedical device comprising: a support member having an outer surfaceoperable to engage an inner surface of an esophagus of a patient; atleast one electrode coupled to said outer surface of the support memberand operable to apply an electrical signal to a vagus nerve of thepatient through the wall of the esophagus, wherein said at least oneelectrode penetrates the wall of the esophagus; a signal generatorcoupled to the support member and to the at least one electrode, whereinsaid signal generator is capable of generating said electrical signalfor application to a vagus nerve of the patient; and a power supplycoupled to said support member and to said signal generator, whereinsaid power supply is capable of providing electrical power to saidsignal generator.
 14. The implantable medical device of claim 13 whereinat least a portion of said signal generator and said power supply areintegral to said support member.
 15. The implantable medical device ofclaim 14 wherein said at least a portion of said signal generator andsaid power supply are embedded within said support member.
 16. Theimplantable medical device of claim 13 wherein said support membercomprises at least one of: a polymer selected from the group consistingof a silicone polymer, a hydrogel, polyethylene, polypropylene,polyurethane, polycaprolactone, polytetrafluoroethylene (PTFE), andcombinations thereof; and a metal.
 17. The implantable medical device ofclaim 13 further comprising a retainment member coupled to said supportmember, said retainment member selected from the group consisting of astent, a metallic ring, a metallic partial ring, a metallic wire, ametallic mesh, a polymer ring, a metallic partial ring, and a polymermesh.
 18. A medical device system comprising: a support member having anouter surface that is adapted to engage an inner surface of an esophagusof a patient; at least one electrode coupled to said outer surface ofthe support member and adapted to apply a therapeutic electrical signaltrans-esophageally to a vagus nerve of a patient, wherein said at leastone electrode penetrates the wall of the esophagus; a signal generatorcoupled to the support member and to the at least one electrode, whereinsaid signal generator is capable of generating said electrical signalfor application to a vagus nerve; a power supply for providingelectrical power to said signal generator; and an external programmingsystem for programming one or more parameters defining said therapeuticelectrical signal.
 19. The medical device system of claim 18 whereinsaid power supply is coupled wirelessly to said signal generator. 20.The medical device system of claim 18 wherein said at least oneelectrode, said signal generator, and said power supply are integratedinto a unitary implantable medical device for implantation in the loweresophagus of the patient.
 21. The medical device system of claim 18wherein said support member comprises at least one of: a polymerselected from the group consisting of a silicone polymer, a hydrogel,polyethylene, polypropylene, polyurethane, polycaprolactone,polytetrafluoroethylene (PTFE), and combinations thereof; and a metal.22. The medical device system of claim 18 wherein said externalprogramming system comprises a programming device selected from thegroup consisting of a personal computer, a personal digital assistant,and a portable computing device.